s1 = 'python代码'
print(len(s1))
print(s1[0], s1[1], s1[-1], s1[-2])
print(s1[-8])
s2 = "WelcomeToChina"
print(s2[3:7])
print(s2[-5:])
print(s2[:7])
print(s2[0:15:3])
print(len(s2))
print(s2[::-2])

a = 'hello'
b = "world"
print(a+b)
age = 20
print("this:" + str(age))
print(b * 5)
a += b
print(a)
a = 'user'
a += 'name'
print(a)
